Abstract
Combining reaction and detection in multiphase microfluidic flow is becoming increasingly important for accelerating process development in microreactors. We report the coupling of UV/Vis spectroscopy with microreactors for online process analysis under segmented flow conditions. Two integration schemes are presented: one uses a cross-type flow-through cell subsequent to a capillary microreactor for detection in the transmission mode; the other uses embedded waveguides on a microfluidic chip for detection in the evanescent wave field. Model experiments reveal the capabilities of the integrated systems in real-time concentration measurements and segmented flow characterization. The application of such integration for process analysis during gold nanoparticle synthesis is demonstrated, showing its great potential in process monitoring in microreactors operated under segmented flow.
Highlights
As PTFE is less wetted by water than by decane, decane was seen as the carrier phase with encapsulated water droplets, the length of which is normally several times the capillary diameter (Fig. 4a)
For nitrogen–water segmented flow, the front and rear ends of a nitrogen bubble were concave in shape due to the hydrophobic nature of PTFE with water, implying the absence of a liquid film surrounding the bubble body (Fig. 4b). This is in contrast to the decane–water segmented flow in which the water droplet ends were convex in shape and a liquid film was present between the droplet and the capillary microreactor wall due to the good wetting of PTFE by decane
We have described the use of a cross-type flow-through cell coupled with capillary microreactors as a convenient means to enable online UV/Vis analysis under segmented flow conditions
Summary
Microreactors have been increasingly utilized on the laboratory scale for developing novel chemical transformations that are more sustainable than the existing routes and for producing materials with desirable structures/ properties hardly accessible using conventional techniques.[1,2,3,4,5,6] The use of microreactors offers many advantages for chemical production including advanced process control (e.g., well-defined flow pattern, uniform temperature distribution, fast response, and increased safety) and substantial process intensification (e.g. enhanced mass transport and improved chemistry).[7,8] In this field, there is a continuous requirement for the integration of process analytical tools with microreactors, which will allow for real-time analysis and subsequently lead to a faster and often more reliable process optimization as compared to the cases with only off-line analysis.9,101-decene in a falling film microreactor[12] and by Keybl and Jensen for investigating the rhodium-catalyzed gas–liquid hydroformylation of 1-octene in a microreactor operated under segmented flow conditons,[13] both using infrared spectroscopy. The above results indicate that the current cross-type flowthrough cell allows a sensing path length much larger than the capillary microreactor diameter for the spectroscopic analysis of the carrier liquid if the fiber tip is arranged further away from the surface plane of the microreactor wall, enabling one to achieve a lower limit of detection.
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